Method and apparatus for automated launch, retrieval, and servicing of a hovering aircraft

ABSTRACT

An aircraft capable of thrust-borne flight can be automatically retrieved, serviced, and launched. In one embodiment, for retrieval, the aircraft drops a tether and pulls the tether at low relative speed into contact with a horizontal guide. The tether is pulled across the guide until the guide is captured b an end effector. The tether length is adjusted as necessary, and the aircraft swings on the guide to hang in an inverted position. Translation of the tether along the guide then brings the aircraft to a docking carriage, in which the aircraft parks for servicing. For launch, the carriage is swung upright, the end effector is released from the guide, and the aircraft thrusts into free flight. A full ground-handling cycle can thus be accomplished automatically with a simple, economical apparatus. It can be used with low risk of damage and requires moderate accuracy in manual or automatic flight control.

PRIORITY CLAIM

This patent application is a continuation of, and claims priority to andthe benefit of, U.S. patent application Ser. No. 13/037,436, filed onMar. 1, 2011, which claims priority to and the benefit of U.S.Provisional Patent Application No. 61/317,803, filed on Mar. 26, 2010,now expired, the entire contents of each of which are incorporatedherein by reference.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application relates to the following commonly-owned pendingpatent applications: U.S. patent application Ser. No. 13/743,069, filedon Jan. 15, 2013, Attorney Docket No. 025100-0022; U.S. patentapplication Ser. No. 13/899,172, filed on May 21, 2013, Attorney DocketNo. 025100-0025; U.S. patent application Ser. No. 13/901,283, filed onMay 23, 2013, Attorney Docket No. 025100-0026; U.S. patent applicationSer. No. 13/901,295, filed on May 23, 2013, Attorney Docket No.025100-0027; U.S. patent application Ser. No. 13/717,147, filed on Dec.17, 2012, Attorney Docket No. 025100-0021; U.S. patent application Ser.No. 13/900,191, filed on May 22, 2013, Attorney Docket No. 025100-0024;and U.S. patent application Ser. No. 13/527,177, filed on Jun. 19, 2012,Attorney Docket No. 025100-0016.

BACKGROUND

1. Field of Invention

The present invention addresses launch, retrieval, and servicing of ahovering aircraft, especially in turbulent winds or onto anirregularly-moving platform, such as a ship in a rough sea. Theinvention is especially suited to unmanned aircraft of small size. Itallows for a fully automated operations cycle, whereby the aircraft canbe repeatedly launched, retrieved, serviced, and re-launched, withoutmanual intervention at any point, and while requiring only modestaccuracy in piloting.

2. Description of Prior Art

Hovering aircraft, be they helicopters, thrust-vectoring jets,“tail-sitters”, or other types, usually land by gently descending infree thrust-borne flight onto a landing surface, coming to rest on anundercarriage of wheels, skids, or legs. This elementary technique canbe problematic in certain situations, as for example when targeting asmall, windswept landing pad on a ship moving in a rough sea. Thewell-known Beartrap or RAST (Stewart & Baekken 1968) as well as theharpoon-and-grid system (Wolters & Reimering 1994) are used to permitretrieval with acceptable safety in such conditions. These systemsrequire an expensive and substantial plant in the landing area, as wellas manual operations coordinated between helicopter and shipboard crew.Furthermore the helicopter must carry a complete undercarriage inaddition to the components necessary for capturing the retrievalapparatus.

Desirable improvements relative to such existing systems include (a)simplification of apparatus, and (b) automated rather than manualoperation. Ideally automation would encompass not only retrieval butalso subsequent refueling and launch. This would be particularlydesirable for an unmanned aircraft, whose operations cycle could then bemade fully autonomous. Some experimental work toward this objective hasbeen done for a hovering aircraft by Mullens, et al. (2004), but withlimited success even with light wind and a stationary base. The presentinvention by contrast provides for fully automated operation in calm orrough conditions, using apparatus which is simple, portable, andsuitable for a small vessel or similarly confined base.

SUMMARY

In one embodiment of the present invention, an aircraft would proceedautomatically from free thrust-borne flight through retrieval,servicing, and subsequent launch through the following sequence ofactions.

-   -   a. While approaching base at low relative speed in substantially        thrust-borne flight, the aircraft drops a tension element such        as a tether or cable, which is typically attached to the        aircraft at a point below the aircraft's mass centre.    -   b. The aircraft then brings the tether into contact with a guide        element such as a crossbar or cable, whose principal dimension        extends horizontally or substantially horizontally across the        approach path of the aircraft and tether.    -   c. The tether is then drawn across the guide until the tether        becomes attached to the guide or a fixture thereon, for example        by a hook on the end of the tether. The aircraft may then adjust        the tether length, or the position of the tether along the        guide, while remaining attached to the guide.    -   d. The aircraft then swings around the guide into an inverted        position, such that its mass centre is below the guide.    -   e. The aircraft then shortens the tether, and translates along        the guide into a docking carriage. Precise positioning in the        docking carriage may be aided by aligning surfaces or by        adjustments in tether length.    -   f. As a consequence of insertion into the docking carriage, or        as a subsequent step, the aircraft may connect to refueling or        other services in the base station. The aircraft's powerplant        may also be shut down.    -   g. At some point the docking carriage is swung upright, so that        the thrust line of the aircraft is pointed upward or        approximately upward.    -   h. The aircraft is refueled and otherwise serviced as necessary        through one or more servicing connectors.    -   i. The tether is disconnected from the guide.    -   j. The aircraft powerplant may be restarted, and launch        preparations completed. The aircraft may then use its own thrust        to pull itself out of the docking carriage into thrust- borne        free flight, or it may be forcibly ejected.

Since loads can be low during retrieval from hover, the apparatus can belight and portable. Furthermore, easy targeting makes the techniquewell-suited for both manual control and economical automation.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1A, 1B, 1C, 1D, 1E, 1F, and 1G are a series of perspective viewsof an embodiment of the present invention for a hovering “tail-sitter”aircraft, showing the aircraft sequentially:

-   -   a. contacting a horizontal guide with a tether, the guide in        this case taking the form of a cylindrical beam;    -   b. capturing the guide;    -   c. swinging around the guide into an inverted position;    -   d. entering a docking carriage;    -   e. swinging in the docking carriage back to an upright position;    -   f. starting its engine, and releasing its hook from the guide;        and    -   g. launching into free flight.

FIG. 2 is a perspective view of one embodiment of a hook used to attachthe tether to a horizontal guide beam or cable.

FIG. 3 is a perspective view of another embodiment of a hook whichincorporates rolling elements to enable translation with low frictionalong a horizontal guide.

FIGS. 4A, 4B, and 4C are a series of perspective views of arepresentative docking carriage, showing:

-   -   a. the carriage by itself;    -   b. an aircraft entering the carriage; and    -   c. the carriage and aircraft swinging around the horizontal        guide.

FIGS. 5A and 5B are a pair of perspective views of a representativefueling connection, showing the connection when (a) open; and (b) mated.

FIGS. 6A, 6B, and 6C are a series of perspective views showing onemechanism for releasing the hook of FIG. 2 from a cylindrical horizontalguide.

FIG. 7 is a perspective view of an embodiment of the base station, inwhich the horizontal guide is a cable.

FIG. 8 is a perspective view of one mechanism for releasing the hook ofFIG. 3 from a cable guide as in FIG. 7.

FIG. 9 is a diagrammatic perspective of an embodiment of the basestation, in which the horizontal guide takes the form of a chain whichruns on a bar, and in which the chain is captured by the aircraft usinga ball on the end of the tether.

FIG. 10 is a diagrammatic perspective view showing one mechanism forreleasing the ball of FIG. 9 from the chain.

DETAILED DESCRIPTION

FIG. 1 shows an illustrative embodiment of the present invention, asused with a “tailsitter” or “tilt-body” aircraft which adopts anose-vertical orientation for thrust-borne flight. For thrust, in thisexample, aircraft 1 uses a main rotor 2, and for attitude control itapplies a combination of variable blade pitch on the main rotor withvariable power on wing-tip thrusters 3.

In preparation for retrieval, the aircraft uses an onboard winch toextend a tension element such as a lightweight tether 4 having aneffector or end fitting 5, which in this embodiment takes the form of ahook as shown in FIG. 2. The aircraft approaches a horizontal guidecomprising a crossbar 6 along an approximately horizontal path at lowrelative speed. This brings the tether into contact with the crossbar asshown in FIG. 1( a). In one embodiment a screen 7 or other suitablefixture may be suspended below the crossbar to damp pendulousoscillations of the tether, which would otherwise cause contact with thecrossbar to be intermittent. After contact is made, the aircraft candraw the hook 5 against the crossbar by some combination of (1)continued translation along the approach path; (2) climb; or (3)retraction of the tether. The crossbar is thereby pulled through thegate 8 of the hook as shown in FIG. 2, and the crossbar is then capturedby the aircraft as shown in FIG. 1( b).

Note, however, that if the hook fails to capture the crossbar then theaircraft will continue unimpeded in thrust-borne free flight, and canreturn for another approach.

In most practical cases the tether will be attached to the aircraftbelow the aircraft mass centre. Hence, once attached to the horizontalguide, the aircraft can be maintained upright only by appropriateapplication of active control to counter inverted-pendulum instability.Control authority, however, may be insufficient to reject disturbancescaused by wind gusts or base motion (as on a rocking ship). Sensitivityto such disturbances increases as tether length decreases. A tetherattachment on the aircraft, as illustrated in FIG. 1, is thereforeproblematic if the aircraft is required to remain upright after capture.However this problem is turned into a virtue by having the aircraftswing inverted as shown in FIG. 1( c). In the inverted position, hangingfrom the guide, the aircraft can handle relatively large disturbances.The swing can be done immediately after capture, or later. For example,the aircraft may rotate after the tether is shortened while the aircraftremains upright. Inverting with a short tether has the advantage ofminimizing the crossbar height necessary to clear underlying obstacles.Once inverted, the aircraft can reduce thrust while maintainingattitude-control authority.

The next step is to translate along the guide toward a docking carriage12. If the guide has sufficiently low sliding friction, or if the hookhas rollers or effective rolling elements, as illustrated in FIG. 3,then the aircraft can pull the tether along-guide by tilting its thrustaxis. Alternatively, the guide can incorporate a mechanism fortranslating the tether. For example, the crossbar of FIG. 1 and FIG. 2is wound with a screw thread 9 whose crests engage the hook. Spinningthe crossbar, for example with a motor 10, thus draws the aircraft alongthe crossbar toward a docking carriage 12. The docking carriage is shownin detail in FIG. 4( a).

As the aircraft approaches the docking carriage, the aircraft can beguided into alignment by various constraining surfaces, including forexample arms 11, longerons 13, and wing trailing-edge supports 14, asshown in FIG. 1( d) and FIG. 4( b). When the tether reaches anappropriate position along the crossbar, the aircraft can winch itselffirmly and precisely into the docking carriage. The aircraft'spowerplant may then be switched off.

In the embodiment of FIG. 1, the docking carriage includes a linkage 16,as shown in more detail in FIG. 5, whereby winching the aircraft intothe carriage causes a fueling probe 17 to be inserted into a receptacle18 on the aircraft. Connections for oil or electricity could be madesimilarly, or by a suitable mechanism actuated independently afterdocking is complete. The aircraft can be serviced through suchconnections at any time while in the docking carriage. For example, fuelmay be pumped from a tank 19 on the base station through a supply line42 into the aircraft. The aircraft or docking station could includeappropriate sensors for measuring flow and quantity so that a specifiedamount of fuel could be automatically on- or off-loaded.

In preparation for launch of the aircraft, the docking carriage must beswung upright. In the embodiment of FIG. 1( e) and FIG. 4( c), this isdone by a telescoping actuator 20 and linkage 21. As the carriageswings, the guide arms 11 rotate under gravity around hinges 22, thusclearing a path for the aircraft to launch without fouling the empennage23. The aircraft meanwhile remains constrained by the longerons 13 andwing supports 14.

When convenient, the aircraft powerplant could be started by an onboardmotor, or by an external motor coupled to the engine by a suitablelinkage. Pre-launch checks could then be executed automatically.

For launch, the hook 5 must be released from the guide 6. One method forhook release is shown in FIG. 6. First, the tether is extended so that apatch of Velcro or like material 26 on the hook's gate 8 comes intocontact with a mating pad 27 wrapped around the crossbar 6, as shown inFIG. 6( a). Then the motor 10 slowly spins the crossbar 6. Meanwhile,the material 26 on the hook's gate 8 and the mating pad 27 remain incontact, and so in effect “unwrap” the gate from the crossbar, as shownin FIG. 6( b). Hence the hook drops away from the crossbar, and can beretracted into the aircraft as illustrated in FIG. 6( c).

The aircraft is then restrained only by gravity and the remainingcarriage constraints. These could be configured to have some appropriatebreak-out force, so that the aircraft could exit into free flight onlyif it had some selected excess of thrust over weight. This would ensurethat, upon pulling free of the docking carriage, the aircraft wouldaccelerate briskly away from the base station and any nearby obstacles.The carriage 12 would then be swung to the inverted position inpreparation for the next retrieval.

For automated operation, the aircraft and base station could each beequipped with satellite navigation or comparable equipment formeasurement of relative position and velocity in three dimensions, usingantennas on the aircraft 28 and on a reference point 29 near the dockingcarriage. Each could also have magnetic or inertial sensors formeasurement of orientation, as well as appropriate mechanisms forcomputation, power supply, and communication.

Other illustrative embodiments are shown in FIG. 7 through FIG. 10. Theembodiment of FIG. 7 uses a tensioned cable 30 as the horizontal guide.This has the advantage of being light and easily packed for transport.The cable could be strung from the docking carriage to a support pole31, or to a support-of-opportunity, such as a tree. The apparatus wouldbe used as previously described, with the aircraft using thrust-tilt topull a rolling-element hook, such as the one shown in FIG. 3, along theguide. For hook release the end of the cable could be fitted with aconcentric cylindrical section 32, as shown in detail by FIG. 8. Thehook would be pulled over the cylindrical section as the aircraftentered the docking carriage. The aircraft could then be released by thesame sequence of steps as described with respect to FIG. 6, with thecylindrical section being spun by the motor 10.

FIG. 9 shows a further alternative embodiment in which the horizontalguide is formed by a chain 33 on a bar 34. One advantage of thisembodiment is that the end-effector on the tether can be a simple bob 37rather than the hook as in FIG. 2 or FIG. 3. For retrieval, the aircraft1 deploys its tether 4 and draws it at low relative speed across thebar. The tether enters one of the apertures formed by teeth 35 attachedto the links of the chain, and thence is channeled into the slot 36between the teeth. The tether is then pulled through the slot until thebob meets the teeth. To complete capture, the aircraft must then swinginverted on the side of the bar opposite the ball. Note that thisconstraint does not apply with the embodiments of FIG. 1 and FIG. 7, inwhich capture is completed before inversion, and which allow theaircraft to invert on either side of the bar.

After inversion, the chain is retracted by a motor 10 into a stowagearea 38 until the ball reaches the vicinity of the docking carriage 12.The aircraft can then park as described above. The carriage is thenswung upright, which must be done in the direction that reverses theaircraft inversion (again this condition does not apply with theembodiments of FIG. 1 and FIG. 7). The ball can then be released. Thiscould be done as shown in FIG. 10, whereby further retraction of thechain 33 pulls the tether along a ramp 39, which ejects the ball 37 fromthe teeth 35. The aircraft can then retract the tether, and launch asdescribed earlier.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention is claimed as follows:
 1. An apparatus comprising: (a) asuspension support; (b) a docking carriage supported by the suspensionsupport and configured to receive a flying object: (c) a flying objectcapturer suspended by the suspension support, the flying object capturerincluding at least two teeth configured to capture a portion of thefling object therebetween; and (d) a motor operatively coupled to theflying object capturer and configured to move the flying object capturerrelative to the suspension support.
 2. The apparatus of claim 1, whereinthe flying object capturer includes a first set of two teeth and asecond different set of two teeth, wherein the teeth of the first setare configured to capture the portion of the flying, object therebetweenand the teeth of the second set are configured to capture the portion ofthe flying object therebetween.
 3. The apparatus of claim 1, whichincludes a guide supported by the suspension support, the guidesupporting the flying object capturer.
 4. The apparatus of claim 3,wherein the motor is configured to move the flying object capturerrelative to the guide.
 5. The apparatus of claim 1, wherein thesuspension support suspends the flying object capturer in asubstantially horizontal orientation.
 6. The apparatus of claim 1,wherein the portion of the flying object includes a flexible member. 7.The apparatus of claim 1, wherein the motor is configured to, after theportion of the flying object is captured, move the flying objectcapturer toward the suspension support until the docking carriagereceives the flying object.
 8. The apparatus of claim 1, Wherein thedocking carriage includes at least one constraining surface configuredto guide the flying object into the docking carriage.
 9. The apparatusof claim 8, wherein the at least one constraining surface includes atleast one of: an arm a longeron, and a wing trailing-edge support. 9.The apparatus of claim 1, wherein the docking carriage is configured toservice the flying object after receiving the flying object.
 10. Theapparatus of claim 8, wherein said servicing is performed automatically.11. The apparatus of claim 9, wherein the docking carriage is configuredto service the flying object via a fueling probe insertable into areceptacle of the flying object.
 12. The apparatus of claim 11, whereinthe fueling probe is configured to add fuel to the flying object andremove fuel from the flying object.
 13. The apparatus of claim 9,wherein the docking carriage is configured to service the flying objectvia an oil connector insertable into a receptacle of the flying object.14. The apparatus of claim 13, Wherein the oil connector is configuredto add oil to the flying object and remove oil from the flying object.15. The apparatus of claim 1, wherein the docking carriage is configuredto service the flying object via an electricity connector insertableinto a receptacle of the flying object.
 16. The apparatus of claim 1,wherein electricity connector is configured to charge a power source ofthe flying, object.
 17. The apparatus of claim 1, which includes one ormore sensors configured to measure at least one of (a) a position of theflying object relative to the apparatus, (b) a velocity of the flyingobject relative to the apparatus, and (c) an orientation of the flyingobject.
 18. apparatus of claim 1, wherein the flying object capturerincludes a chain.
 19. An apparatus comprising: (a) a suspension support;(b) a docking carriage supported b the suspension support and configuredto receive. a flying object; (c) a flying object capturer suspended bythe suspension support, the flying object capturer including at leasttwo teeth configured to capture a portion of the flying objecttherebetween; and (d) a motor operatively coupled to the flying objectcapturer and configured to, after the portion of the flying object iscaptured, move the flying object capturer toward the suspension supportuntil the docking carriage receives the flying object.
 20. An apparatuscomprising: (a) a suspension support; (b) a docking carriage supportedby the suspension support and configured to receive a flying object; (c)a flying object capturer suspended by the suspension support in asubstantially horizontal orientation, the flying object capturerincluding a first set of two teeth and a second different set of twoteeth, wherein the teeth of the first set are configured to capture aportion of the flying object: therebetween and the teeth of the secondset are configured to capture the portion of the flying, objecttherebetween; and (d) a motor operatively coupled to the flying objectcapturer and configured to, after the portion of the flying object iscaptured, move the flying object capturer toward the suspension supportuntil the docking carriage receives the flying object.